Conventionally, various studies have been made for a monitoring technique for displaying an image capturing a dark area. For instance, there is known a television camera including an image capturing lens, image capturing (pick-up) devices having sensitivity ranging from the near infrared light to the visible light, an IR (infrared) cut filter for eliminating wavelength components in the near IR range, and a video image signal processing means for generating black and white signals and color signals according to video signals from the image capturing devices (see Patent Document 1). This television camera includes also a filter exchanger means. With this filter exchanger means, if the photographic object has a luminance lower than a predetermined luminance, the IR cut filter is exchanged by a dummy glass (blank glass) to generate black and white video signals. On the other hand, if the photographic object has a luminance higher than the predetermined luminance, the dummy glass is exchanged by the IR cut filter to generate color video signals. Further, with this television camera, during the period of determination of filter exchange, a still image before the filter exchange is outputted to a monitor or the like.
According to this technique of Patent Document 1, when the photographic object has low luminance, its image is captured without using the IR cut filter, so a black and white video image is outputted. On the other hand, if the photographic object has high luminance, its image is captured with using the IR cut filter, so that a color video image is outputted. With this arrangement, with for a dark object, an image having as high as possible luminance can be obtained.
Further, as another technique, there is known an automatic exposure apparatus for a car-mounted camera to be mounted on an automobile vehicle having a variable beam projection type headlight configured to maintain the illumination by the headlight to the traveling direction of the vehicle (see Patent Document 2). This automatic exposure apparatus for a car-mounted camera includes a car-mounted camera for capturing an image of a predetermined area around the vehicle body, a photometric area setting means for setting a photometric area in such a manner that an image of the used area for a image captured by the car-mounted camera may be an image captured under appropriate exposure, a steering angle/illumination direction information obtaining means for obtaining at least one of information about a steering angle of the steering wheel and information about the illumination direction of the beam of the headlight, and an illumination area captured image estimating means. This illumination area captured image estimating means, based on the information obtained by the steering angle/illumination direction information obtaining means, estimates an occupying area, within the image capturing area of the car-mounted camera, of an illumination area image capturing area, which is an area for use in capturing the image of the area illuminated by the beam of the headlight, the estimation including presence/absence of the illumination area image capturing area within the image capturing area of the car-mounted camera. The photometric area setting means is cable of varying the photometric area according to change in the result of estimation by the illumination area captured image estimating means.
With this technique of Patent Document 2, an appropriate exposure adjustment is realized by varying the photometric area for use in the exposure adjustment according to the illumination area of the headlight.
As still another technique, there is known a side monitoring camera system for an automobile, including an image capturing means for capturing an image of at least a side (lateral) area of the front portion of the vehicle, a light mounted to the vehicle and capable of illuminating at least the side area of the vehicle front portion, and a controlling means for controlling the illumination condition of the light according to the image capturing state of the image capturing means (see Patent Document 3). With this technique of Patent Document 3, as the image capturing area is illuminated by the light, a bright image can be captured.